Spectral Studies on the Interaction between Mercuric Ion and ApoCopC

The interaction between mercuric ion and apoCopC in the absence or presence of cupric ion was investigated through difference UV spectra in Hepes buffer （10 mmol·L^-1） at pH 7.4. The results suggest that mercuric ion can bind to C- and N-terminal binding sites of apoCopC, and the conditional binding constants were calculated to be kN=（6.79± 1.12）× 10^6 mol^-1·L and kc=（3.06±0.05）× 10^5 mol^-1·L. Using urea as a chemical agent, the conformational stabilities of apoCopC and HgN^2＋ -CopC-Hgc^2＋ were monitored by fluorescence spectrum in Hepes buffer （50 mmol·L^-1） at pH 7.4. The free energy of stabilization is （14.69±0.85） and （16.66±0.55） kJ.mol^-1, respectively. HgN^2＋ -CopC-Hgc^2＋ is more stable than apoCopC.     

Selective detection of mercury(II) and methylmercury(II) via coordination-induced emission of a small-molecule probe

Mercury is one of the major toxic pollutants and has many adverse effects on human health. The main mercury species in the environment or in living organisms are inorganic mercuric ion (Hg²⁺) and organic methylmercury (CH3Hg+). Detection of the two mercury ions is a particularly active topic in the molecular sensing field during the past decade. However, efficient sensors that can sensitively detect and discriminate the two species are rare. In this work, we adopt the concept of restriction of intramolecular rotations which is the basis of aggregation induced emission, and design a molecular probe with pyridyl group as the chelating unit and 1,8-naphthalimide as the fluorescent unit for the detection of both Hg²⁺ and CH₃Hg⁺. When the probe is free in solution, it exhibits weak fluorescence because free intramolecular rotations of the 1,8-naphthalimide moieties non-radiatively annihilate its excited state. However, upon coordination with Hg²⁺ or CH₃Hg⁺, the rotation of 1,8-naphthalimide moieties would be restricted due to the chelation between 1,8-naphthalimide and Hg²⁺ or CH₃Hg⁺, leading to significantly enhanced fluorescent emission. The response induced by Hg²⁺ is much stronger than CH₃Hg⁺; but for specific detection of CH₃Hg⁺, we introduced a T-rich DNA fragment which could completely mask Hg²⁺ in solution. Furthermore, we have employed the sensor for confocal imaging of Hg²⁺ and CH₃Hg⁺in immobilized cells. We expect the probe design tactics can be generally useful for sensing many other analytes.     

A microcalorimetric study of the action of mercuric chloride on the metabolism of mitochondria isolated from Cyprinus carpio liver tissue

After the occurrence of 'Minamata disease' in 1950, mercury aroused much more attention, and lots of studies concerned have been made. The purpose of the present paper is to study the effect of mercuric chloride on the mitochondria suspension isolated from the liver tissue of Cyprinus carpio from the direct viewpoint of energy by using the microcalorimetric method. The metabolic thermogenic curves of the mitochondria suspension at 25°C were obtained, and the mitochondria metabolic thermokinetic equations were established, from which we obtained the thermodynamic and thermokinetic parameters: thermogenic rate constant (k), heat output (Q), average heat power (P_av), etc. Experimental results indicated that low concentration of mercuric chloride (5 nmol Hg²⁺/(mg protein)) stimulates the thermogenesis of mitochondria, suggesting a strong effect of uncoupling action, while high concentration of mercuric chloride (20 nmol Hg²⁺/(mg protein)) inhibits the metabolism of mitochondria completely, suggesting a fatal effect on the phosphorylation system. The effect of Hg²⁺ on mitochondria is concentration-depended, from which the probable reaction mechanism of Hg²⁺ to the mitochondria was proposed. So the microcalorimetric method can be used in the toxicology research.     

Oligonucleotides-based biosensors with high sensitivity and selectivity for mercury using electrochemical impedance spectroscopy

A novel electrochemical biosensor with high sensitivity and selectivity for mercuric ion detection, based on DNA self-assembly electrode, is designed. Thiol functionalized poly-T oligonucleotides were used as gold electrode modifier through formation of Au–S bond between DNA and gold electrode. In presence of Hg²⁺ ions, the specific coordination between Hg²⁺ and thymine bases can change parallel ss-DNA from linear to hairpin structures, which can cause the release of partial DNA molecules from the surface of the electrode. The density of DNA on the surface of electrode correlated with the concentration of mercury in the solution and can be monitored by electrochemical impedance spectroscopy. The limit of detection of this method is pM level of mercuric ions which is far below the upper limit of Hg²⁺ mandated by United States Environmental Protection Agency (EPA), 2 ppb (10 nM). In addition, this method showed excellent selectivity. A series of divalent metal ions, including Ni²⁺, Co²⁺, Mg²⁺, Zn²⁺, Ba²⁺ and Cd²⁺, have little interference with the detection of Hg²⁺.     

Metal-Triggered DNA Folding by Different Mechanisms

Metal-mediated base pairs by the interaction between metal ions and artificial bases in oligonucleotides has been widely used in DNA nanotechnology and biosensing technique. Using isothermal titration calorimetry, circular dichroism spectroscopy and fluorescence spectroscopy, the folding process of T-C-rich oligonucleotides (TCO) induced by Hg²⁺ and Ag⁺ with the synthetic sequence d(T₆C₆T₆C₆T₆C₆T₆) was studied and analyzed. Although thermodynamic data predict that TCO should initially fold into a relatively stable hairpin through two possible pathways of conformational transitions whether Hg²⁺ or Ag⁺ were added at first, the mechanisms and final products between the two are entirely different from isothermal titration calorimetry outcomes. When Hg²⁺ were added first, the haipin was formed through T-Hg-T structure with further stabilization by C-Ag-C after Ag⁺ addition. However, it is proposed that an unusual metal-base pair for Ag⁺ binding is generated instead classical C-Ag-C when Ag⁺ was injected first. Moreover, further confirmation of this unconventional metal-base pair T-Ag-C was verified by circular dichroism and fluorescence spectroscopy.     

A new Hg2+ fluorescent sensors based on 1,3-alternate thiacalix[4]arene (L) and the complex of [L+Hg2+] as turn-on sensor for cysteine

A new thiacalix[4]arene derivative in a 1,3-alternate conformation bearing four naphthalene groups through crown-3 chains has been synthesized, which exhibits high selectivity toward Hg²⁺ by forming a 1:2 complex, among other metal ions ( Na⁺, K⁺, Mg²⁺, Ba²⁺, Ca²⁺, Sr²⁺, Cs⁺, Mn²⁺, Fe²⁺, Cd²⁺, Co²⁺, Ni²⁺, Cu²⁺, Li⁺, and Zn²⁺) with a low detection limit (3.30×10^?7 M). The metal ion-binding properties were studied by fluorescence, AFM, and ¹H NMR spectroscopy. The in situ prepared [Hg²⁺+L] complex shows well recognition ability for cysteine with a low detection limit (2.23×10^?7 M) through fluorescence turning on. The mechanism of fluorescence turning on is the host L releasing from [L+Hg²⁺] for [Cys+Hg²⁺] complex formed. Thus the paper reports secondary-sensor design: Hg²⁺ as a first sensor for [L+Hg²⁺] form, cysteine as a second sensor for Hg²⁺ releasing from the [L+Hg²⁺] complex after cysteine adding in.     

铜转运蛋白C端金属结合域与Ag+及Hg2+的相互作用

铜转运蛋白(CTR1)不仅参与铜的细胞摄取,而且在其它重金属离子的摄取过程中也发挥重要作用. 本文采用紫外-可见(UV-Vis)光谱,核磁共振(NMR)和质谱(MS)的方法,研究了人源CTR1 (hCTR1)的C端金属结合域(C8)与Ag⁺和Hg²⁺的相互作用. 研究表明,Ag⁺和Hg²⁺都能与C8结合,但二者与C8的结合机制明显不同. 每个C8分子可以结合两个Ag⁺离子,但一个Hg²⁺却可以与两个C8形成桥联. 此外,Ag⁺离子与C8的配位是一个中等速度的交换过程,而Hg²⁺离子则为快速交换过程. C8的半胱氨酸残基是两种离子的重要结合位点,同时组氨酸残基也参与两种金属离子的配位,其中Ag⁺优先结合组氨酸,而Hg²⁺则对半胱氨酸的结合具有显著的优势. 虽然HCH基序对C8 与金属配位至关重要,一些远端的其它氨基酸也可以参与C8 与银离子的配位,这可能与CTR1 在摄取Ag⁺过程中的金属转移机制相关. 这些结果为理解hCTR1 蛋白摄取重金属离子的作用机制提供了必要的信息.     

Mercuric ions induced aggregation of gold nanoparticles as investigated by localized surface plasmon resonance light scattering and dynamic light scattering techniques

With the development of nanosciences, both localized surface plasmon resonance light scattering (LSPR-LS) and dynamic light scattering (DLS) techniques have been widely used for quantitative purposes with high sensitivity. In this contribution, we make a comparison of the two light scattering techniques by employing gold nanoparticles (AuNPs) aggregation induced by mercuric ions. It was found that citrate-stabilized AuNPs got aggregated in aqueous medium in the presence of mercuric ions through a chelation process, resulting in greatly enhanced LSPR-LS signals and increased hydrodynamic diameter. The enhanced LSPR-LS intensity ( I) is proportional to the concentration of mercuric ions in the range of 0.4-2.5 M following the linear regression equation of I = 84.7+516.4c, with the correlation coefficient of 0.983 (n = 6) and the limit of determination (3 ) about 0.10 M. On the other hand, the increased hydrodynamic diameter can be identified by the DLS signals only with a concentration of Hg 2+ in the range of 1.0-2.5 M, and a linear relationship between the average hydrodynamic diameters of the resulted aggregates and the concentration of Hg 2+ can be expressed as d = 6.16 + 45.9c with the correlation coefficient of 0.994. In such case, LSPR-LS signals were further applied to the selective determination of mercuric ions in lake water samples with high sensitivity and simple operation.     

Dulplex analysis of mercury and silver ions using a label-free fluorescent aptasensor

Label-free Hg²⁺ aptamer was used as a sensing element and the PicoGreen dye was specific to ultra-sensitive double-stranded DNA (dsDNA), which achieved novel fluorescence assay for detection of both mercury and silver ions. In this aptasensor, Hg²⁺ bound to thymidine (T) to form T–Hg^2+-T base pairs and Ag⁺ specifically interacted with C–C mismatches to produce C–Ag⁺–C base pairs. The conformation changes prevented the aptamer from binding to its complementary sequences to form dsDNA and caused a fluorescence intensity decrease with PicoGreen. The change in the fluorescence intensity made it possible to detect both Hg²⁺ and Ag⁺ in a dose-dependent manner. The sensing system could detect as low as 5 × 10^–8 mol/L of Hg²⁺ and 9.3 × 10^–10 mol/L of Ag⁺. The fluorescent intensity changes in the system were specific for Hg²⁺ and Ag⁺, making this simple and cost-effective method extremely valuable in its future applications in monitoring Hg²⁺ and Ag⁺ pollution in environmental analysis.     

A self-assembled tetrapeptide that acts as a “turn-on” fluorescent sensor for Hg2+ ion

The tetrapeptide (Bz-$\mathrm{\Delta }$Phe(p-NPh₂)-l-DOPA(protected)-l-Phe-l-Phe-OMe was designed to incorporate seven phenyl rings so that it’s conformation, self-assembly and application in Hg²⁺ ions sensing could be studied. Peptide molecules adopted an overlapping β-turn of type III/III conformation in crystals. The peptide showed a highly selective turn-on response towards mercuric ion over other metal ions with a 10-fold enhancement in fluorescence intensity. This intensity change coupled with the selectivity of the peptide towards mercury allowed us to demonstrate simple colorimetric dip sensing of Hg²⁺ ions. The technique provides a highly selective and effective way to detect Hg²⁺ ions. The peptide also self-assembled into nanospheres with diameter ranges from 100 to 500?nm. Mercuric ion coordination enabled these peptide nanospheres to aggregate into well-defined nanoparticles. The enhanced fluorescence upon Hg²⁺ addition demonstrates that peptide scaffolds can be exploited in the development of different selective sensors.     

A ratiometric electrochemical biosensor for sensitive detection of Hg based on thymine–Hg–thymine structure

In this paper, a simple, selective and reusable electrochemical biosensor for the sensitive detection of mercury ions (Hg²⁺) has been developed based on thymine (T)-rich stem–loop (hairpin) DNA probe and a dual-signaling electrochemical ratiometric strategy. The assay strategy includes both “signal-on” and “signal-off” elements. The thiolated methylene blue (MB)-modified T-rich hairpin DNA capture probe (MB-P) firstly self-assembled on the gold electrode surface via Au–S bond. In the presence of Hg²⁺, the ferrocene (Fc)-labeled T-rich DNA probe (Fc-P) hybridized with MB-P via the Hg²⁺-mediated coordination of T–Hg²⁺–T base pairs. As a result, the hairpin MB-P was opened, the MB tags were away from the gold electrode surface and the Fc tags closed to the gold electrode surface. These conformation changes led to the decrease of the oxidation peak current of MB (I_MB), accompanied with the increase of that of Fc (I_Fc). The logarithmic value of I_Fc/I_MB is linear with the logarithm of Hg²⁺ concentration in the range from 0.5 nM to 5000 nM, and the detection limit of 0.08 nM is much lower than 10 nM (the US Environmental Protection Agency (EPA) limit of Hg²⁺ in drinking water). What is more, the developed DNA-based electrochemical biosensor could be regenerated by adding cysteine and Mg²⁺. This strategy provides a simple and rapid approach for the detection of Hg²⁺, and has promising application in the detection of Hg²⁺ in real environmental samples.     

Selective fluorescent sensor for mercury ions in aqueous media using a 1,4-dihydropyridine derivative

Novel 1,4-dihydropyridine (DHP) derivatives containing 3 carboxylic acid units are synthesized via cyclotrimerization of N-substituted β-aminoacrylates followed by basic hydrolysis of the triester. These DHP derivatives are readily soluble in aqueous media buffered at pH 8.0 and the solutions give blue fluorescent signals with quantum yields of 7–23%. One of these compounds, bearing a p-methoxyphenyl N-substituted group, shows specific fluorescent quenching with the mercuric ion (Hg²⁺). The fluorescent signal of the DHP derivative decays over a period of minutes to hours depending on the Hg²⁺ concentration, which implies that the sensing mechanism involves chemical reaction between the Hg²⁺ ion and the DHP compound. The ¹H NMR and MS data suggest that Hg²⁺ mediates the oxidation of the DHP ring into a pyridinium ring. The event is useful for fluorescent detection of Hg²⁺ at the micromolar level within 30 min, with a detection limit of 0.2 μM in aqueous medium.     

Ag+与Hg2+对G-四链体DNA结构的破坏及其对构筑DNA逻辑门的应用

本工作利用圆二色光谱研究了Ag+与Hg2+对4种代表性G-四链体DNA结构的破坏作用。结果表明Ag+可能通过与碱基G螯合从而破坏G-四链体结构;Hg2+能通过形成T-Hg2+-T碱基对,及其他方式破坏G-四链体结构。含巯基(-SH)的半胱氨酸与Ag+与Hg2+可以发生较强的配位作用,从而使被Ag+与Hg2+破坏后的G-四链体DNA结构得以回复。基于此,一个新颖的Ag+/Hg2+-半胱氨酸-DNA逻辑门得以构筑。     

Ag+与Hg2+对G-四链体DNA结构的破坏及其对构筑DNA逻辑门的应用

本工作利用圆二色光谱研究了Ag⁺与Hg²⁺对4种代表性G-四链体DNA结构的破坏作用。结果表明Ag⁺可能通过与碱基G螯合从而破坏G-四链体结构;Hg²⁺能通过形成T-Hg²⁺-T碱基对,及其他方式破坏G-四链体结构。含巯基(-SH)的半胱氨酸与Ag⁺与Hg²⁺可以发生较强的配位作用,从而使被Ag⁺与Hg²⁺破坏后的G-四链体DNA结构得以回复。基于此,一个新颖的Ag⁺/Hg²⁺-半胱氨酸-DNA逻辑门得以构筑。     

Ultrasensitive,Rapid, and Selective Detection of Mercury Using Graphene Assisted Laser Desorption/Ionization Mass Spectrometry

We report an extremely sensitive and specific detection of mercuric ions (Hg²⁺) based on graphene assisted laser desorption/ionization mass spectrometry (GALDI-MS). Combining the highly selective coordination interactions between thymine (T) and Hg²⁺, we present a simple, effective, and novel approach, based on π–π interactions of the T-Hg²⁺-T complex and G that can serve as a platform and matrix for GALDI-MS. The present sensor not only exhibits high selectivity and sensitivity (picomolar) to Hg²⁺ in aqueous solution, but also can elucidate the chemical structures of the metal complexes. The significant advantage in the current approach is that there is no need for a sophisticated instrument, and no sample pretreatment is required to detect the Hg²⁺ ions.

A Novel Fluorescent Probe Based on Perylene Derivative for Hg2+ Ions and Biological Thiols and its Application in Live Cell Imaging and Theoretical Calculations

The selective and sensitive detection of biothiols; cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) in aqueous solutions is of considerable importance because of their pivotal roles in maintaining the reducing environment in the cells. This study describes a strategy for the determination of biothiols based on the PDI/Met‐Hg²⁺complex platform. We designed and fabricated methionine modified perylene diimide molecule as a selective sensing probe for Hg²⁺ ions in aqueous solutions ( PDI/Met‐Hg ²⁺). The complex between perylene bisimide derivative ( PDI/Met) and Hg²⁺ was investigated and it demonstrated turn‐on fluorescence response for the detection of the biological thiols. Besides, PDI/Met displayed fluorescence quenching response in the presence of mercury ions and the emission intensity of PDI/Met‐Hg²⁺ was recovered after transferring biothiols (Cys, Hcy, and GSH). Thus, PDI/Met could be utilized as a fluorescent chemosensor for the sequential recognition of mercury ions and biological thiols.     

Affinity of Divalent Mercury Towards Nitrogen Donor Ligands

As with gold, relativistic effects are important in the chemistry of mercury. Together with the closed‐shell d¹⁰ configuration of Hg²⁺ they account for the special bonding schemes as preferred linear coordination with highly covalent contributions to chemical bonding or special affinities to nitrogen and sulfur that are so prominent in mercuric chemistry. This research report summarizes recent research on coordination compounds with halogen, oxygen and, especially, nitrogen as direct bonding partners of divalent mercury and their competition with each other. In a rather systematic way N‐donor ligands with one, two and more than two nitrogen atoms have been inspected in order to elucidate the influences that lead to the special bonding schemes of Hg^II‐N compounds.     

Ratiometric fluorescence detection of mercuric ion based on the nanohybrid of fluorescence carbon dots and quantum dots

A novel nanohybrid ratiometric fluorescence probe comprised of carbon dots (C-dots) and hydrophilic CdSe@ZnS quantum dots (QDs) has been developed by simply mixing the blue-emission C-dots with red-emission carboxylmethyldithiocarbamate modified CdSe@ZnS QDs (GDTC-QDs). The nanohybrid ratiometric fluorescence probe exhibits dual emissions at 436 nm and 629 nm under a single excitation wavelength. Due to the strong chelating ability of GDTC on the surface of QDs to mercuric ion (Hg²⁺), the fluorescence of the GDTC-QDs in the nanohybrid system could be selectively quenched in the presence of Hg²⁺ while the fluorescence of the C-dots remained constant, resulting in an obviously distinguishable fluorescence color evolution (from red to blue) of the nanohybrid system. The detection limit of this method was found to be as low as 0.1 μM. Furthermore, the recovery result for Hg²⁺ in real samples including tap water and lake water by this method was satisfying, suggesting its potential application for Hg²⁺ sensing.     

Silver nanoparticles embedded cation-exchange membrane for remediation of Hg species and application as the dip catalyst in organic transformation

Silver nanoparticles (Ag NPs) embedded in poly(perfluorosulfonic) acid cation-exchange membrane (Nafion-211) were synthesized by in situ reductions of Ag⁺ ions by sodium borohydride at room temperature and formamide at 65 °C. The formamide-reduction formed Ag NPs uniformly distributed in the membrane matrix. Therefore, the formamide-reduced Ag NPs embedded membranes were used for the sorption-preconcentration of Mercury (Hg)²⁺ ions by the galvanic reaction with Ag NPs in the membrane matrix. The replacement of Ag⁰ in NPs with Hg²⁺ ions resulted in the formation of Hg⁰ accumulated as nanodroplets in the membrane matrix as indicated by the field emission scanning electron microscopy studies. The sorption of Hg²⁺ ions via galvanic reaction in the Nafion membrane was found to be maximum (>93%) from pH = 2.5 to pH = 6.5. The Ag NPs embedded membrane was studied for Hg²⁺ ions sorption from the aqueous samples by radiotracer (²⁰³Hg), spectrophotometry, energy dispersive X-ray fluorescence and cold vapor atomic absorption spectrophotometry. This membrane was successfully applied for the determination and quantification of Hg²⁺ ions in the real water samples and safe storage of Hg for the remediation objective. The Hg⁰ embedded membrane was also found to be promising as the dip catalyst in the representative organic transformation of phenylacetylene to acetophenone. The Hg⁰ embedded membrane dip catalyst was reused in four consecutive cycles under similar conditions and found to be successful by giving an almost similar yield (%) of the product. This demonstrated a possibility of safe application of Hg⁰ stored in the matrix of poly(perfluorosulfonate) membrane for catalysis.     

A Novel Modified Carbon Paste Electrode for Potentiometric Determination of Mercury(II) Ion

A new modified carbon paste electrode (CPE) based on a recently synthesized ligand of Ethyl‐2‐(benzoylamino)‐3‐(2‐hydroxy‐4‐methoxyphenyl)‐2‐propenoate (EBHMP) as a suitable carrier for Hg²⁺ ion was described. The electrode exhibit a super Nernstian slope of 48.5±1.0 mV per decade for Hg²⁺ ion over a wide concentration range from 3.0×10^?7–3.1×10^?2 M. The lower detection limits are 1.0×10^?7 M Hg²⁺. The electrode has a fast response time (ca. 5 s), a satisfactory reproducibility and relatively long life time. The proposed sensor shows a fairly good selectivity toward Hg²⁺ ion in comparison to other common cations. The potentiometric responses are independent of the pH of the test solution in the pH range 1.0–4.0. The proposed electrode was used as an indicator electrode in potentiometric titration of mercuric ion with standard solution of EDTA. The direct determination of mercury in spiked wastewater and an amalgam sample gave results that compare favorably with those obtained by the cold vapor atomic absorption spectrometric method.